1. Field of the Invention
The present invention relates to the field of exercise devices, and more particularly to automated exercise machines capable of providing positive and negative exercises.
2. Prior Art
In the field of muscular development, a variety of theories exist for achieving maximum muscular development. A great number of exercise devices are available, each focussing its functionality to one or more of these theories. For example, isokinetic devices regulate or control the rate of muscular contraction regardless of the force applied to the device by a user's muscular contraction. For example, in an isokinetic device where a weight is attached to a bar and where the user initiates actions with the bar, the isokinetic device only regulates the speed of the movement of the bar. U.S. Pat. No. 4,483,532 teaches the use of a centrifugal brake to increase movement resistance as the velocity of the exercise bar is increased above some preset value. U.S. Pat. No. 4,363,480 teaches the use of a centrifugally regulated frictional resistance device to control the speed of a treadmill regardless of the amount of force exerted by the user.
Another class of devices provide for positive only non-eccentrically loaded use. These devices provide for the regulation of the resistance force against the user, only when the bar is moving, but do not control the bar speed during the exercise, such as when a muscle contracts during a positive exercise. For example, U.S. Pat. No. 4,354,676 teaches the use of a computer controlled valve to regulate the internal pressure of a hydraulic cylinder connected to the exercise bar. U.S. Pat. No. 4,609,190 teaches the use of a double acting hydraulic cylinder with an assorted control valve for each cylinder to resist the exercise bar movement by providing a different resisting force for resisting movement. However, most of these hydraulic devices provide for positive exercise only.
Whereas many of these positive only exercise devices utilize a hydraulic cylinder to vary the resistance force, some machines use an electrically controlled friction brake which is typically coupled between the exercise bar and the user. The resisting force is varied by the amount of friction applied to a rotating member on the exercise bar. U.S. Pat. No. 4,261,562 teaches the use of a DC generator as a variable force resistance device in which the electrical loading coupled to the generator is varied. U.S. Pat. No. 4,063,726 also utilizes a hydraulic cylinder and having an electronically controlled valve to vary the resistance force.
A third category of exercise devices deals with positive and negative stroke operating devices. This category contains a wide variety of mechanical, electronic, and electro-mechanical devices to provide exercise in both positive and negative directions. For example, U.S. Pat. No. 3,858,873 provides for a use of a spiral cam coupled between the exercise bar and a stack of metal weights to provide an increasing force during a positive exercise stroke. U.S. Pat. No. 3,848,467 uses a speed controlled motor in the negative stroke and a friction brake in the positive stroke of an exercise. U.S. Pat. No. 4,569,518 utilizes a variable torque transmitting clutch for both positive and negative stroke control. U.S. Pat. No. 4,235,437 teaches the use of a hydraulic pump and electrically controlled valves to vary the force or the speed of positive and negative strokes.
Although various exercise devices are described above in relation to a number of example exercise categories, most of these devices stress a particular type of exercise for achieving maximum muscle development. It is generally known that maximum isolation of a given muscle by a particular exercise device produces the greatest amount of strength increase during exercise. Secondly, because the strength of the muscle varies, depending on its degree of contraction, and because the amount of force that the muscle can apply varies by the bone-joint angle, the resisting force must vary as a function of the contraction of the muscle to attain maximal strength gained during the exercise.
The various exercise devices described above, although based on various exercise theories, provide for muscular development by providing a resistive force to a contracting muscle. Muscle contraction can be generally classified as being concentric, isometric, or eccentric. Concentric contraction refers to a situation of the muscle when it shortens its length. A simple example of concentric contraction is when a weight is lifted from a rest position. Because the weight is accelerated from its initial position, positive work is achieved as the contracting muscle expends energy in lifting the weight. This is referred to as positive exercise.
Isometric contraction occurs when two forces are at equilibrium so that movement cannot occur. Although work is not performed, the muscle under contraction still expends energy in counteracting the other force. Isometric contraction provides for a holding exercise, which is neither positive or negative. A third type of contraction is eccentric contraction. A simple example is the lowering of a weight to its rest position. In eccentric contraction, the weight is decelerated and the total work performed is negative because the muscle absorbs energy in decelerating the weight. Therefore negative exercise is performed by eccentric contraction. In eccentric contraction, muscle is lengthened from its contracted or previously contracted position. That is, the muscle is being lengthened by a load or a force greater than the muscle's holding force.
In a concentric contraction exercise, positive strength is used in which the muscle is shortened against a force or resistance, such as in lifting a weight. In a concentric exercise system, also called a positive exercise system, an object is moved by the muscular contraction, such as by lifting, so that it will cause the muscle to expend energy and this energy is stored in the object. In this instance, the lifting force of the muscle must exceed the resistive force of the object. When the force expended by the muscle equals the weight of the object, this holding strength of the muscle provides the isometric contraction. In an isometric contraction, no movement occurs but energy is expended by the muscle.
An eccentric exercise involving negative strength will occur when the force exerted by the muscle is less than the resistive force of the object, which was previously lifted. As the object is lowered, the potential energy stored in the object is converted to kinetic energy and absorbed by the muscle. The muscle lengthens from the previously contracted position. An eccentric exercise system is based on a force overcoming a contracted muscle. That is, the force (weight) is greater than the muscle's holding force.
It is generally known that not only is the direction of exercise important, but emphasis is placed on the type of resistive force (or load) opposing the muscle to be exercised. An eccentric load provides a stretching or pulling force against the contracting muscle and can occur during positive or negative exercise stroke. An eccentrically loaded exercise system is one in which an object moved by the muscular contraction stores this energy, not merely dissipating it, that is the exercise system possesses potential energy which is available to do work on the contracted muscle whenever the muscle force becomes less than the force supplied by the exercise machine.
In actual life, the combination of eccentric and concentric contractions operate together, such as when lifting and lowering a weight. Further, the combination of eccentric and concentric contractions form a natural type of muscle function called a "stretch-shortening cycle". The stretch-shortening cycle allows the concentric contraction to take place with greater force or power output, as compared to initiating a movement by concentric contraction alone. This phenomenon is believed to occur partly due to the elastic nature of the muscle during and immediately after the eccentric contraction. The lengthening of the contracted muscle modifies the condition of the muscle such that the stretched muscle increases its tension and stores potential energy. Part of this stored energy can be recovered provided that the concentric contraction occurs rapidly after the eccentric contraction.
Further, in comparing negative exercise to positive exercise, negative only exercise produces at least as much, if not greater, muscle growth than positive only exercise. Strength increase of as much as 40% has been documented by the use of negative exercise (Ettington Darden; The Nautilus Bodybuilding Book; Chapters 13-14; Contemporary Books, Inc,; 1982). Furthermore, the negative exercise provides other advantages, such as stretching for the improvement of flexibility; pre-stretching for high-intensity muscular contraction; resistance in the position of full contraction for full range exercise; and maximum application of resistance throughout a full range of possible movement.
Additionally, not only is the direction of the exercise a critical factor, but the speed of the velocity of the exercise in both directions is also extremely important. This factor will determine the rate of muscular contraction and lengthening during the exercise phase. Further, peak mechanical efficiencies of different types of muscle fibers occur at different velocities of shortening. For example, the maximum efficiency of fast twitch fibers appears to appear at high contractive speeds, whereas slow twitch fibers show corresponding peak efficiency at lower contraction speeds (Goldspink G; Energy Turnover During Contraction of Different Types of Muscle; Biomechanics; pp 27-39; University Park Press; 1978). Therefore, the individual's ideal rate of contraction and lengthening can be determined by strength testing of the muscle at various speeds.
It is appreciated than that what is needed is an exercise device that provides for both positive and negative exercises with eccentric loading, provides variable positive and negative forces, controls the speed of the device in both directions, and also provides for the testing of the muscle for positive and negative strength at various speeds.